The invention relates to storm mapping systems.
Over the past 25 years, the aviation industry has been the beneficiary of improved storm mapping systems. See U.S. Pat. Nos. 4,023,408 and 4,395,906. Those storm mapping systems took advantage of the correlation between thunderstorms and lightning discharges. The violent air currents that are hazardous to aircraft flight produce the lightning discharge. The lightning discharge also generates electromagnetic radio waves. Directional receiving apparatus, located on board an aircraft, can determine the direction of the lightning discharge. Some information is available about the distance of the discharge as well. By receiving and storing this direction and distance information, a map is formed from the stored data, to give the pilot a plan view image of the storm activity relative to the aircraft.
From the inception of the popularity of these devices, it was known that there was a significant difference in the precision with which distance and direction was determined. In particular, direction was precise but distance was not. Various attempts have been made to eliminate the imperfect distance estimate. The present invention is premised on the conclusion that all of the prior efforts have fallen short of what is necessary.
Accordingly, the invention provides an enhanced weather mapping system for determining location of lightning related weather activity relative to a moving platform, such as an aircraft. The invention employs a receiver on board the platform which is responsive to electrical signals generated by the lightning in a predetermined frequency band. Associated with the receiver are means for determining the azimuth of a source of the electrical signals relative to the receiver. The data, indicating the azimuth from the receiver to the signal source is stored. After the platform has moved, the stored azimuth information is updated so as to correct for the motion of the receiver. Finally, a determination of weather pattern location is obtained by combining updated azimuth indications with more current azimuth information for estimating the location of a weather pattern at the intersection of a more current azimuth indication and an updated azimuth indication. Because the motion of the platform (i.e. the aircraft) is typically at a much higher rate than the motion of the weather activity, there is minimal error introduced by ignoring any weather motion.
More particularly, the invention can readily be explained as a unique application of well known triangulation. It is well known, indeed there are storm mapping systems which are based on, triangulation. As applied to weather mapping or storm mapping, triangulation is typically employed by determining the azimuth from a first location to weather activity and then determining the azimuth from a second location to the weather activity. Only one more piece of information is necessary to uniquely determine the location of the weather activity and that is the distance and direction which separate the two locations. The foregoing description has described triangulation in distance, i.e. where there is some distance between the two sensing locations.
The present invention is an application of triangulation in time, i.e. where there is but a single sensing location which is a moving platform, and that platform senses direction between the platform and the weather pattern at two different points in time.
The art is well aware of the equipment necessary to determine azimuth from a receiver to a source of electrical signals related to a lightning strike. The invention relies on use of any suitable apparatus to perform this function. It is also well known that triangulation requires two different measurements to be made. In accordance with the present invention, those two different measurements are measurements of azimuth between the moving receiver and the weather pattern. Before those two different measurements can be compared in a triangulation operation, one of the measurements must be adjusted to account for the change in position of the receiver due to the lapse in time between the two different measurements. More particularly, the first measured azimuth is updated to account for the motion of the receiver between the time of the first measurement and the time of the second measurement.
The motion of the platform can be measured or estimated in any of a number of ways with fairly good precision. This information is used to update the azimuth of the first measurement in a manner which will be described. Having been updated, it is then only necessary to combine the azimuth of the second measurement with the updated azimuth of the first measurement to locate the weather pattern in a manner that will be described. Accordingly, in one respect the invention comprises:
a system for estimating the location of a lightning related weather pattern relative to a moving platform, comprising:
a receiver, supported on the platform, responsive to electrical signals generated by the lightning in a predetermined frequency band;
first means responsive to the output of the receiver for determining the azimuth of a source of the electrical signals relative to the platform;
memory means coupled to the first means for storing an indication of the azimuth;
second means for updating the stored indications to correct for motion of the platform so as to provide an updated azimuth indication; and
third means for combining stored and updated azimuth indications for estimating the location of the weather pattern at the intersection of an azimuth indication and an updated azimuth indication.
In another respect, the invention comprises:
a method of enhancing an estimate of the location of a lightning related weather pattern relative to a moving platform, comprising:
receiving, on the platform, electrical signals generated by the lightning at a predetermined frequency band;
repeatedly determining from the received signals, the azimuth of a source of the electrical signals relative to the platform;
storing at least one indication of the azimuth from at least one said determination;
updating one or more stored indications to correct for the motion of the platform to provide at least one updated indication; and
combining at least one stored and at least one updated indication for estimating the location of the weather pattern as the intersection of a memory indication and an updated memory indication.